Field of the Invention
The present invention relates to a power transmission system of a hybrid electric vehicle, and more particularly, to a power transmission system of a hybrid electric vehicle capable of increasing a usage of a mechanical power transfer path by transferring a larger torque than an engine torque to an output shaft and maximally using power of an engine in a hybrid mode.
Description of Related Art
An environmentally-friendly technology of a vehicle is a core technology which controls a survival of a future automobile industry and advanced car makers have focused their own energy on the development of an environmentally-friendly vehicle to achieve environment and fuel efficiency regulations
Therefore, each car maker has developed an electric vehicle (EV), a hybrid electric vehicle (HEV), a fuel cell electric vehicle (FCEV), and the like, as a future vehicle technology.
As described above, since the future vehicle has several technical restrictions such as weight, cost, and the like, the car makers have paid attention to the hybrid electric vehicle as an alternative to solve realistic problems such satisfaction of exhaust gas regulations and enhancement of fuel efficiency performance and are fiercely competing to commercialize the hybrid electric vehicle.
The hybrid electric vehicle is a vehicle using more than two power sources and may be combined in several ways. Here, as the power source, a combination of a gasoline engine or a diesel engine using traditional fossil fuel and a motor/generator driven by electrical energy is used.
The hybrid electric vehicle may be implemented as an EV mode driven only by a motor, an HEV mode simultaneously using the engine and the motor, and an engine mode using only the engine, depending on a combination of an engine and a motor.
Further, the hybrid electric vehicle drives a power generator using kinetic energy of a vehicle, instead of using idle stop stopping the engine at the time of stopping the vehicle and using braking by the existing friction at the time of braking the vehicle. In this case, it is possible to more remarkably enhance fuel efficiency than the typical vehicle due to fuel saving, and the like by regenerative braking to store electrical energy generated by the driving of the power generator in a battery and reuse the stored electrical energy at the time of driving.
As described above, a power transmission system of a hybrid electric vehicle is classified into a single mode scheme and a multi-mode scheme.
The single mode scheme may not require torque transfer mechanisms, such as a clutch and a brake, for a shift control, but may have reduced efficiency at the time of high-speed driving and thus low fuel efficiency and require an additional torque amplifier for applying to a large vehicle.
The multi-mode scheme may have high efficiency at the time of high-speed driving and may be designed to amplify a torque, and as a result, may be applied to a medium and large size vehicle.
Recently, therefore, the multi-mode scheme rather than the single mode scheme has been mainly adopted and thus a study thereon has been actively conducted.
The power transmission system based on the multi-mode scheme is configured to include a plurality of planetary gear sets, a plurality of motors/generators used as a motor and a power generator, a plurality of torque transfer mechanisms (friction elements) which may control rotation elements of the planetary gear set, a battery used as the power source of the motor/generator, and the like.
The power transmission system based on the multi-mode scheme has different operation mechanisms depending on a connection configuration of the planetary gear set, the motor/generator, and the toque transfer mechanism.
Further, the power transmission system based on the multi-mode scheme is different in durability, power transmission efficiency, a size, and the like depending on the connection configuration, and therefore in the field of the power transmission system of the hybrid electric vehicle, research and development to implement more robust, compact power transmission system without power loss has been continued.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.